This application relates generally to steering columns and more particularly to a responsive energy absorbing device for steering columns.
Many steering column assemblies today are equipped with kinetic energy absorption devices to reduce the likelihood of injury in case of an accident. Such devices come in many different forms. One form that is particularly effective in absorbing significant quantities of energy in a relatively small amount of space employs a plastically deformable member such as a metal strap which is bent over an anvil. In the event of a head-on collision, the deformable strap is drawn across the anvil and the deformed shape travels along the length of the strap, causing a reaction force resisting collapse of the steering column and absorbing energy.
Typically, energy absorbing devices, such as those employing a plastically deformable strap, are designed to protect drivers of average weight in a collision of average severity, without taking into account the fact that all drivers are not of average weight and that collisions vary considerably in severity depending on vehicle speed at the time of the impact.
In accordance with the present invention, it is possible to vary the reaction force resisting collapse of the steering column. For example, the energy absorbing device of this invention may provide a smaller amount of resistance in the case of a less severe collision or a lower weight driver, or a greater amount of resistance in the case of a more severe collision or a driver of greater weight. Whether the driver is seated close to the steering wheel, or belted, are also factors to be considered in determining the desired amount of reaction force.
The resistance is preferably provided by a plastically deformable strap having one end portion bent around an anvil. The anvil is connected to the steering column and the other end portion of the strap is connected to stationary vehicle support structure, or vice versa. This arrangement forms a linkage between the steering column and the vehicle support structure so that when the steering column collapses in a collision, the strap will move over the anvil and resist such collapse. Often two or more such straps similarly arranged are provided. By breaking one or more of such linkages, the associated strap will drop out of the system so that the overall resistance to collapse is reduced depending upon conditions detected by a controller either before or at the instant of the collision.
In one form of the invention, the linkage is broken by a knife operable to bisect the associated strap. Preferably, the knife is actuated by an explosive charge which is ignited by a signal generated by the controller. In another form of the invention, the linkage is broken by an explosive charge which severs one of the connections. The explosive charge in this form of the invention is also ignited by the signal from the controller. One such connection may include a reduced neck portion of the anvil and the explosive charge may be disposed in a hollow interior of the anvil adjacent to the neck portion.
In yet another form of the invention, an energy absorbing strap extends around a piston which has two or more different size anvils. The piston is axially slidable in a cylinder to positions surrounding one or another of the anvils. The strap is drawn over the anvil it surrounds when the steering column collapses, thereby resisting collapse of the steering column and absorbing a certain amount of energy depending on the size of the anvil.
One object of this invention is to provide an energy absorbing device having the foregoing features and capabilities.
Other objects, features and advantages of the invention will become more apparent as the following description precedes.